1. Field of the Invention
The present invention relates to a biological detection device, a fingerprint authentication device, and a biological detection method for discriminating whether a test body is a living body or not. Specifically, the present invention relates to a biological detection device and the like which discriminate a test body with a high degree of accuracy, while achieving reduction of the costs and miniaturization of such devices.
2. Description of the Related Art
In recent years information equipment such as a portable phone and PDA (Personal Digital Assistance) are capable of storing a large amount of individual information and also can be connected to networks. Therefore, a higher level of security has been demanded in such information equipment.
In response to such a demand, individual authentication using biological information (biometrics information) has become widely implemented, since passwords or the like could be stolen. Particularly, use of fingerprints as the biological information is highly convenient.
When individual authentication is carried out using fingerprints, a fingerprint (a pattern constituted by ridge lines which contact a fingerprint sensor and valley lines which do not contact) is obtained as image information from a fingerprint sensor, then characteristic information is extracted from the image information, and the extracted characteristic information is compared with a characteristic information of an individual to be authenticated, which is registered in advance. In this way the individual authentication is performed.
However, in recent years an artificial finger with a counterfeit fingerprint has been created and unfairly used. Therefore, when individual authentication is carried out using fingerprints, prevention of improper use of such artificial fingers is strongly desired.
For a conventional technology of preventing improper use of the counterfeit fingerprint, there is disclosed a biological detection device in which a test body oscillating frequency generating portion generates oscillating frequency corresponding to the electrostatic capacity of the test body, and a biological control portion detects whether the test body is a living body or not on the basis a reference signal for judging whether the test body, which is set in advance, is the living body or not (for example, the following Japanese Patent Application Laid-Open No. H10-165382).
Furthermore, there is also disclosed a biological detection device in which a voltage application portion applies two square-wave input voltages having different frequencies to a finger, and impedance of the finger is computed from an output voltage obtained in response to the application of the square-wave input voltages, to check whether the impedance is within the range of stored impedances of the reference living finger, whereby it is determined whether the finger is the living body or not (for example, the following Japanese Patent Application Laid-Open No. 2005-143804).
However, in Japanese Patent Application Laid-Open No. H10-165382, only the electrostatic capacity is used to detect whether the finger is the living body or not. For this reason, for example, if using a gummy matter (a substance obtained by gelling gelatine solution), which strongly resembles human skin, the electrostatic capacity which is close to that of a human finger may be obtained, thus there is a problem that a counterfeit finger can be created relatively easily.
In Japanese Patent Application Laid-Open No. 2005-143804, on the other hand, since the voltages with two different frequencies are applied to a finger from the voltage application portion, two oscillators are required inside the voltage application portion. Moreover, biological determination and the like are required to be performed in accordance with the output voltages of the different frequencies, thus control circuits for performing switching and the like are also required to be installed in a biological determination portion. Therefore, Japanese Patent Application Laid-Open No. 2005-143804 has a problem that miniaturization of the device and reduction of costs are difficult due to a large number of parts. In addition, Japanese Patent Application Laid-Open No. 2005-143804 further has a problem that complicated formulae are required to be executed to compute impedance of the finger, slowing the processing time.